CHICAGO — It wasn’t that long ago that Jacoby Ellsbury was easily the Yankees’ best player.
Now, he doesn’t wear that crown due to a 1-for-23 slump that included an 0-for-4 in Tuesday night’s 6-1 loss to the Cubs.

“He has struggled a bit. He is kind of in between,’’ manager Joe Girardi said. “He is a guy who was so good in the first five weeks of the season and he is in a little funk now. We have to get him going, he is a big part of our offense.”

In addition to being hitless in four at-bats, Ellsbury was 0-for-3 with runners in scoring position.

Adam Warren has experience as a starting pitcher, but Girardi said he isn’t planning any changes in his rotation in the wake of losing CC Sabathia for at least six more weeks with a knee problem.

“Right now we will stay in turn, whatever that is,’’ Girardi said before ace right-hander Masahiro Tanaka lost the opener of a two-game series against the Cubs. “We will stay in turn and the last time through they all threw the ball pretty well so we need that to continue.’’

In the previous five games — two against the Mets and three versus the Pirates — Yankees starters went 3-0 with a 1.47 ERA and allowed 22 hits in 30 ²/₃ innings. Of course, Tanaka helped those numbers out by throwing a complete-game shutout against the Mets May 14.

Since the rotation houses Frontier League (Independent) alumni Vidal Nuno and Chase Whitley, who has made one start, those numbers aren’t expected to continue, but Warren has developed into a key piece of the bullpen and Girardi likely doesn’t want to mess with what has clearly been the team’s strongest department so far.

As for Sabathia, Girardi said he doesn’t know when he will return, but he isn’t expecting him anytime soon. Sabathia is on the disabled list with a degenerative issue in the right knee that has been treated with cortisone and stem cell injections. At best, Sabathia will be out until July.

“It’s going to take some time,’’ Girardi said. “I don’t have an exact number but when you are out for a while … I don’t necessarily thing he would have to start over but he is going to have to make rehab starts.’’

Former Cub Alfonso Soriano spent Monday night visiting with Starlin Castro, the Cubs’ talented shortstop and continued to hammer home the point he tried to get across to him when they were teammates.

“I went to his apartment and we had a good time,’’ said Soriano, who was dealt by the Cubs to the Yankees last July. “I told him how good it was to play here and to try and get better every day. To be a good player and do all the little things to get better. He has the talent to be a superstar. He has the tools.’’

Soriano was greeted with polite applause by Cub fans and went 0-for-4.

Sitting in the opposing dugout Tuesday night at Wrigley Field, Girardi reiterated he had no desire to leave The Bronx when his contract expired after last season. The Cubs were interested, but Girardi only had eyes for the Yankees who gave him a four-year deal worth $16 million.

“We talked to the Yankees solely,’’ said Girardi, an East Peoria, Ill. native who played at Northwestern and made his major league debut in 1989 with the Cubs. “[New York] is the place we wanted to be and the place we call home. For us it was making sure the Yankees wanted us back.’’

Rightfully so the biggest concern around the Yankees is a starting staff that won’t have Ivan Nova for the rest of the season and nobody can predict when Sabathia and Michael Pineda will return.

Yet, a lack of clutch hitting has hurt the lineup.

Going into Tuesday night’s game against the Cubs at Wrigley, the Yankees .249 average with runners in scoring position was 12th among the 30 MLB clubs. However, their .655 OPS was 24th and their .305 on-base percentage was 24th. In comparison, the Mets were 12 in OPS at .716 and 10th in on-base with a .340 mark.

The biggest culprits outside of Carlos Beltran, who is on the disabled list, were Soriano, Brian Roberts and Derek Jeter. Soriano was batting .162 (6-for-37) with runners in scoring position, Roberts was at. 200 (6-for-30) and Jeter was hitting .216 (8-for-37). Of those combined 20 hits the only extra base hit was a double by Roberts.

On the other side, Yangervis Solarte was batting .333 (12-for-36) with 20 RBIs with runners in scoring position, Brett Gardner was at .382 (13-for-34) and Mark Teixeira was hitting .320 (8-for-25).